In times past when concern about safety was less developed, workers on roofs simply accepted the risk of falling and carried out their tasks without safety harnesses or safety rails.
In more enlightened times, requirements have been set forth that all workers at risk of falling must be protected. In many cases this is done by harnesses and fall restraint cables but often this is restrictive, particularly where there are a number of workers in the area to be protected.
An alternative approach is to provide a safety fence around the perimeter of the area. A number of proposals have been made to provide such a construction. Typically this is done by constructing a full scaffolding around the perimeter but this is expensive and time consuming. Alternative constructions have been provided but often these do not provide sufficient stability.